1. Field of the Invention
This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to the kinematic arrangement of planetary gearing, clutches, brakes, and overrunning couplings for such transmissions.
2. Description of the Prior Art.
This invention comprises a transaxle assembly having a hydrokinetic torque converter and multiple ratio gearing for use with an internal combustion vehicle engine. In a preferred embodiment, the engine and the transaxle are mounted in a common powertrain package with the axis of the crankshaft of the engine in alignment with the axis of the hydrokinetic torque converter. The multiple ratio planetary gearing is mounted on the output shaft axis, which is arranged in parallel with the converter axis. The engine and output shaft axis may be mounted transversely in the forward vehicle engine and transaxle compartment of a front wheel drive vehicle with forward traction wheels.
Various arrangements of gearing, clutches, brakes, and couplings for multiple-speed ratio power transmissions include two planetary gear units having some of their components mutually interconnected and another planetary gear unit, or pair of meshing pinions and gears, located between the engine and the two planetary gear units. Input speed to the two planetary gear units is provided either through a direct drive connection to the engine or through a gear mechanism that underdrives the input. Therefore, torque applied to the components of the two planetary gear units is greater than it would be if the input were driven at a higher speed. Consequently, those components and the friction elements that control them are larger and heavier than if torque carried by them were lower.
Examples of multiple-speed planetary gear units having a two-speed input are described in U.S. Pat. Nos. 5,039,305; 5,250,011; 5,267,913; and 5,267,916.
It is preferable to overdrive the inputs to the multiple-speed gear units so that torque carried by them and the associated control members is reduced. This permits a reduction in size and weight of the components located at the rear of the gear box.
Hydraulically actuated friction clutches require rotary hydraulic seals to minimize leakage and related losses. Since both of the members are drivably connected by a clutch rotate, use of rotary seals is extensive to avoid leakage and the resulting variation of gear shift quality. Furthermore, clutches frequently require balance dams to minimize adverse effects of centrifugal pressure head induced by rotation.
A friction brake connects one rotating member to a nonrotating member, usually the transmission housing. The brake piston does not rotate. Therefore, because a brake requires less hydraulic sealing, it is preferable to minimize the number of clutches required to control operation of the gear mechanism and to substitute, wherever possible, a brake for a clutch.